1. Field of the Invention
The present invention relates to systems deployed on-site on land or at sea for the acquisition of geophysical data.
2. Description of the Related Art
These systems use an assembly of sensors, linked by electrical cables to casings whose role is to process the data emanating from the sensors, in particular by digitizing the data and transmitting them to a central processing unit to which the casings are also linked by electrical cables. These casings can also comprise means making it possible to test the operation of the sensors and the digitizing of the data.
The known systems are generally designed according to one of the following two architectures, which will now be explained with reference to FIGS. 1 and 2:
monotrack architecture (represented in FIG. 1),
multitrack architecture (represented in FIG. 2).
FIG. 1 is a diagram representing a monotrack architecture. In this diagram, the geophysical data acquisition system S comprises a plurality of tracks T(i), each of which consists of an assembly of geophysical sensors.
Such tracks T(i) are well known and conventionally consist of n identical modules which each link in series or in parallel m geophysical sensors such as geophones whose analog output signal characterizes the response of the subsurface strata to the signal emitted following the activation of one or more seismic sources.
The monotrack system S also comprises casings B(i) for digitizing the analog data emanating from the sensors of each track, and transmitting these data to storage means (not represented in the figure). Each track T(i) is thus linked to a respective casing B(i) by a cable 10 connected to a port P(i) of the casing, said cable conveying the analog data emanating from the sensors of the track T(i).
The casings B(i) comprise means for digitizing these analog signals, and for transmission to the storage means by way of a cable C which links the casings in series.
The cable C is composed of sections C(i) conveying the digital signals emanating from the casings B(i) as well as the electrical power supply required for the operation of these casings. Each section C(i) is furnished at each of its two ends with a connector 20 for coupling R with a casing. Each casing B(i) therefore comprises in addition to its port P(i) two connectors for cooperating with the connectors 20 of two cable sections.
The diagram of FIG. 2 represents a so-called xe2x80x9cmultitrackxe2x80x9d or xe2x80x9cN-trackxe2x80x9d system Sxe2x80x2, according to the second type of architecture commonly employed.
The multitrack system Sxe2x80x2 comprises casings Bxe2x80x2(j) for digitizing and transmitting data, each casing being linked to N tracks T(i) (4 tracks for each casing in the instance of the system represented here, but N-track systems in which N is equal to 6 for example are also commonly used). Each track is for its part linked to a single casing, by way of a cable 10 conveying the analog data emanating from the sensors of the track.
An important difference as compared with the monotrack system S represented in FIG. 1 is that in the instance of the multitrack system, the cables 10 for transmitting analog data are linked to the casings Bxe2x80x2(j) not directly by a port, but by way of a main cable Cxe2x80x2 to which the casings are linked in series and to which the cables 10 are coupled by so-called take-outs E(i) as they are widely known in the art.
The cable Cxe2x80x2 transmits, like the cable C of the monotrack system of FIG. 1, the digital data emanating from the casings to storage means, not represented in the figure.
An N-track system thus comprises N times fewer casings than tracks, each interval between two consecutive casings comprising N take-outs of which the first N/2 are linked to a first of the two casings, the other N/2 take-outs being linked to the second casing.
The cable Cxe2x80x2 of the multitrack system Sxe2x80x2 is more complex that the cable C of the monotrack system of FIG. 1. This cable Cxe2x80x2 thus comprises inside a single sheath:
the extensions of the cables 10 for routing the analog data emanating from the tracks of sensors to the corresponding casing,
conductors for transmitting digital data,
at least one conductor for supplying power to the casings.
The casings Bxe2x80x2(j) are linked to the cable Cxe2x80x2 by connectors of the casing cooperating with matching connectors 20xe2x80x2 of the cable Cxe2x80x2 so as to constitute couplings Rxe2x80x2.
In the two known architectures described hereinabove, the distance between two tracks T(i) is typically of the order of 50 meters. This distance is also that which separates two consecutive casings of a monotrack system, while the casings of an N-track system are separated by around (Nxc3x9750) meters.
These two architectures each comprise advantages and drawbacks, which may be summarized as follows:
The two architectures described hereinabove have moreover common drawbacks:
Firstly, the number of couplings R or Rxe2x80x2 is sizeable, even if this number is reduced in the instance of a multitrack system. Since the data acquisition installations can be moved in the field, one and the same piece of hardware comprising the tracks and the casings is successively deployed and gathered up at various locations, this involving very many operations for making and undoing the multiple couplings of the system. It is therefore understood that this large number of couplings is especially detrimental in terms of cost of labor and timescales.
Another drawback common to both types of system is that each of the casings which they employ comprises two connectors for coupling with a main cable. The presence of these connectors on the casing constitutes a sizeable obstacle to the miniaturization of the casing, while present-day technological developments make it possible to substantially reduce the bulkiness of the other components of the casing. It would nevertheless be advantageous to reduce the size of the casings, which at present constitute voluminous elements of the systems and may be an impediment to the laying and gathering operations.
A third drawback common to present-day systems stems from the fact that it is sometimes necessary to supplement the couplings between the main cable and the casings with load take-up devices, such as portions of tension cables, one end of which is fixed to a part of the electrical cable close to the casing and the other end of which is mounted, in a removable or nonremovable manner, on the casing itself.
This arrangement may be necessary when the assembly formed by the cables and the casings is subjected to tensile loads, for example when submerging the assembly in water traversed by a strong current.
Such load take-up devices increase the complexity and the time required for employing the system, since when mounting and demounting casings provided with removable load take-up devices, the connecting and disconnecting of the electrical cables and of the casings must be accompanied by the mechanical stowing and unstowing of said load take-up devices.
Moreover, the load take-up device (comprising means on the casing, such as for example rings secured to the casing) constitutes just like the connectors an obstacle to the miniaturization of the casings.
Furthermore in the two known types of architecture, it is necessary to handle two families of objects having very different dimensions: the casings and sections of the main cable on the other hand, with specific logistics suited to each family.
However, there is nowadays a desire to gradually move the operations for laying and gathering the acquisition systems toward greater automation, so as to cut the associated labor costs and reduce the duration of these operations. Such movement is made tricky nowadays by the fact of having to handle these two families of objects.
Finally, it has been seen that the two architectures each exhibited drawbacks. The operators must therefore determine, on the basis of the specifics of the geophysical data acquisition campaign to be carried out, the suitable architecture. This implies that in many instances no choice of architecture will be optimal, and that the operators must have access to the hardware required for implementing the chosen architecture, this leading to overequipment or to hiring which is detrimental in terms of costs.
A purpose of the invention is to make it possible to produce systems for acquiring geophysical data which are economical to manufacture and utilize by virtue of the sizeable reduction in the number of connectors employed in these systems.
A second purpose of the invention is to facilitate the operations for laying and gathering the acquisition systems by harmonizing the format of their components (which at present comprise casings and cables, the formats of these two types of components being very different).
A third purpose of the invention is to make it possible to produce a system in which the casings are of substantially smaller dimensions than the dimensions of present-day casings.
Another purpose of the invention is to make it possible to produce systems according to the objectives hereinabove, in which the casings may be subjected to sizeable tensile loads (of the order of 500 Newtons for utilization on land, and of the order of 2 500 Newtons for utilization in a wet environment of the xe2x80x9cshallow waterxe2x80x9d type to use the widespread terminology), while still having reduced dimensions (of the order of 200 cm3)
In order to achieve these purposes, the invention proposes a module for acquiring geophysical signals, comprising:
at least one casing Bxe2x80x3(i), Bxe2x80x3, which houses processing means including means for digitizing the signals,
and two cable sections Cxe2x80x3(i) each comprising:
at a first end, a connector suitable for being coupled up to a complementary connector,
at a second end, an adapter designed to be fixed to the casing and to effect an electrical link with the processing means housed in the casing.
Preferred but nonlimiting aspects of the system according to the invention are the following:
it comprises at least two casings, linked in series by cable segments, comprising at each end an adapter designed to be fixed to the casing and to effect an electrical link with the processing means housed in the casing.
each casing comprises a rigid member fixed on one face of the respective adapters secured to the respective cable sections or segments, so as to take up a sizeable part of the tensile loads exerted between these two cable sections or segments.
each casing comprises means for attaching the adapters of the cables to the rigid member.
the means for attachment are rigid lugs, a part of which is embedded in the adapter, another part of each lug projecting from the adapter toward the rigid member and engaged in a respective orifice of the rigid member along a direction substantially perpendicular to the direction of the part of the cable sections or segments which is adjacent to the casing.
processing means integrated into the cable adapters comprise spark arresters.
the rigid member carries means for processing electrical signals.
each casing comprises leaktightness means.
the leaktightness means comprise a seal placed in a space circumscribed by the lugs.
at least one casing comprises a platen situated on a second face of the cables which is opposite the first face and is substantially parallel to the rigid member.
parts of the lugs which project toward the platen are engaged in orifices of said platen.
the cable section end connectors are mechanically and electrically hermaphrodite and are identical.
the adapter situated at the second end of each cable section is designed to be fixed in a removable manner to a casing.
the casings comprise a port for the connection of at least one geophysical sensor outside the casing.
Other aspects, purposes and advantages of the present invention will become more apparent from reading the following detailed description of a preferred embodiment thereof, given by way of example and with reference to FIGS. 3 to 6b of the appended drawings, in which drawings: